Clean Room Quiz 4

Clean Room Quiz 4

Question: What is the purpose of the airflow test?

Answer: The purpose of the airflow test is to measure airflow velocity, uniformity, and supply air volume flow rate in cleanrooms and clean zones. This includes measuring velocity distribution in unidirectional airflow areas and supply air volume flow rate in non-unidirectional areas.

Question: How is the supply air volume flow rate measured?

Answer: The supply air volume flow rate is measured either downstream of final filters or in air supply ducts. Both methods rely on measuring the velocity of air passing through a known area, with the air volume flow rate calculated as the product of velocity and area. The choice of procedure should be agreed upon between the customer and supplier.

Question: What conditions should be carefully considered when measuring airflow velocity?

Answer: When measuring airflow velocity, the following conditions should be carefully considered:

1. a) The probe direction should be chosen appropriately based on the airflow velocity.
2. b) Measurements should be conducted over a sufficient time for repeatable readings, and the average velocity or air volume flow rate should be recorded.

Question: What does the velocity of the unidirectional flow determine in a unidirectional cleanroom?

Answer: The velocity of the unidirectional flow determines the performance of a unidirectional cleanroom.

Question:  How is the velocity of the unidirectional flow measured in a cleanroom?

A: The velocity of the unidirectional flow can be measured either close to the face of the terminal supply filters or within the room. This is achieved by defining a measuring plane perpendicular to the supply airflow and dividing it into measuring points (grid cells) of equal area.

Question: Where should the airflow velocity be measured?

Answer: The airflow velocity should be measured at approximately 150 mm to 300 mm from the filter face or entry plane.

Question: How is the minimum number of measuring points (grid cells) determined for airflow velocity measurements?

Answer: The minimum number of measuring points (grid cells) is determined by Formula : N = under root 10× A, where N is the minimum number of measuring points (rounded up to a whole number) and A is the measured area in square meters (m²).

Question: How is the average velocity calculated for a zone with unidirectional airflow?

Answer: The average velocity (Va) for a zone with unidirectional airflow is calculated using Formula (B.2): Va = (ΣVn) / N, where Va is the average velocity in meters per second (m/s), ΣVn is the sum of all the measured velocities (Vn) in m/s, Vn is the measured velocity at each of the grid cell centers, and N is the number of locations at which the velocities (Vn) were measured.

Question: Why is it advantageous to increase the number of measuring points (grid cells) for airflow velocity measurements?

Answer: Increasing the number of measuring points (grid cells) can be advantageous when using measured data to determine airflow volume flow rate or uniformity of velocity. It improves the likelihood of detecting uneven airflow velocities, especially in smaller areas.

Question: What considerations should be made regarding the measuring time at each position during airflow velocity measurements?

Answer: The measuring time at each position should be sufficient to ensure a repeatable reading. Time-averaged values of measured velocities should be recorded for multiple locations.

Question:  What risks are associated with measuring the supply airflow velocity too close to or too far from the filter face?

Answer: If the supply airflow velocity is measured too close to the source, there is a risk of measurement error due to variable airflow distribution. Conversely, if measured too far from the filter face, the measurement reading can be compromised.

Question: How can disturbances to unidirectional airflow be mitigated during measurements?

Answer: To exclude disturbances to unidirectional airflow during measurements, a temporary barrier can be used.

Question: What should be confirmed when production apparatus and workbenches are installed?

A: When production apparatus and workbenches are installed, it is important to confirm that significant airflow variations do not occur.

Question: How is the uniformity of velocity (UV) calculated?

Answer: The uniformity of velocity (UV) is calculated using Formula:  UV = [1 − (σ / Va)] ⨯ 100, where σ represents the standard deviation and Va represents the average velocity.

Question: How is the maximum deviation of velocity (Dmax) calculated?

Answer: The maximum deviation of velocity (Dmax) is calculated using the formula:

Dmax = [(Vd – Va) / Va] ⨯ 100, where:

Dmax represents the maximum deviation in percentage.

Va is the average velocity.

Vd is the reading with the most variance from the average velocity.

Question: What does the maximum deviation of velocity indicate?

Answer: The maximum deviation of velocity indicates the extent of variation between the reading with the most variance from the average velocity (Vd) and the average velocity (Va), expressed as a percentage.

Question: How can the total supply air volume flow rate be calculated from the results of the airflow velocity test?

Answer: The total supply air volume flow rate (Q) can be calculated using Formula:

Q = Σ(Vn × Ac), where:

Ac is the cell area defined as the free area of the media divided by the number of measuring points (grid cells) in square meters (m²).

Q is the total air volume flow rate in cubic meters per second (m³/s).

Vn is the airflow velocity at each cell center in meters per second (m/s).

Σ represents the summation for all cells.

Question: What factors can influence the accuracy of the air volume flow rate calculation when using this method?

Answer: The accuracy of the air volume flow rate calculation, when using this method, can be influenced by various factors, such as the choice of test apparatus, choice of measuring locations, number of measuring points (grid cells), distance from the filter face, and calculation of open cell area.

Question: What are the apparatuses mentioned for determining the supply air volume flow rate in air ducts?

Answer: The apparatuses mentioned for determining the supply air volume flow rate in air ducts include orifice meters, Venturi meters, pitot static tubes, and anemometers.

Question: How should the airflow velocity be measured in a rectangular duct using pitot static tubes or anemometers?

A: In the case of measuring airflow velocity in a rectangular duct using pitot static tubes or anemometers, the measuring plane in the duct should be divided into measuring points (grid cells) of equal areas, and the airflow velocity should be measured at the center of each cell. The number of measuring points (grid cells) should be agreed upon between the customer and supplier.

Question: Is it same when measuring supply air volume flow rate between the measuring methods by filter face velocity and measurement in the air duct.

Answer: No, There can be differences between the measuring methods by filter face velocity and measurement in the air duct when measuring the supply air volume flow rate.